Precambrian Research 191 (2011) 58–77
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Precambrian Research 191 (2011) 58–77 Contents lists available at SciVerse ScienceDirect Precambrian Research journa l homepage: www.elsevier.com/locate/precamres The Putumayo Orogen of Amazonia and its implications for Rodinia reconstructions: New U–Pb geochronological insights into the Proterozoic tectonic evolution of northwestern South America a,∗ a b c Mauricio Ibanez-Mejia , Joaquin Ruiz , Victor A. Valencia , Agustin Cardona , a d George E. Gehrels , Andres R. Mora a Department of Geosciences, The University of Arizona, Tucson, AZ, USA b School of Earth & Environmental Sciences, Washington State University, Pullman, WA, USA c Smithsonian Tropical Research Institute, Balboa-Ancon, Panama d Instituto Colombiano del Petroleo ICP, ECOPETROL, Piedecuesta, Santander, Colombia a r t i c l e i n f o a b s t r a c t Article history: Outcrops of late Meso- to early Neoproterozoic crust in northwestern South America are restricted to Received 13 June 2011 isolated exposures of basement inliers within the northern Andes of Colombia, Peru and Venezuela. How- Received in revised form 12 August 2011 ever, evidence for the existence of an autochthonous Stenian–Tonian belt in northern Amazonia that is Accepted 13 September 2011 undisturbed by Andean orogenesis has not been recognized so far. Here we report ∼1200 new single- Available online 17 September 2011 zircon U–Pb geochronological analyses from 19 Proterozoic rock samples of northwestern South America collected from the Garzón and Las Minas Andean cordilleran inliers, drill-core samples from the foreland Keywords: basin basement, and outcrops of cratonic Amazonia in eastern Colombia (western Guyana shield). Our South America Amazonia new geochronological results document the existence of a previously unrecognized Meso- to Neoprotero- zoic orogenic belt buried under the north Andean foreland basins, herein termed the Putumayo Orogen, Putumayo Orogen Rodinia which has implications for Proterozoic tectonic reconstructions of Amazonia during the assembly of the Grenville supercontinent Rodinia. Based on the interpretations of new and pre-existing data, we propose a three- U–Pb geochronology stage tectonometamorphic evolution for this orogenic segment characterized by: (1) development of a pericratonic fringing-arc system outboard of Amazonia’s leading margin during Mesoproterozoic time from ∼1.3 to 1.1 Ga, where the protoliths for metaigneous and metavolcanosedimentary units of the Colombian and Mexican inliers would have originated in a commonly evolving Colombian–Oaxaquian fringing-arc system; (2) amphibolite-grade metamorphism and migmatization between ca. 1.05 and 1.01 Ga by inferred amalgamation of these parautochtonous arc terranes onto the continental margin, and (3) granulite-grade metamorphism at ∼0.99 Ga during continent–continent collision related to Rodinia final assembly. Along with additional paleogeographic constraints, this new geochronological framework suggests that the final metamorphic phase of the Putumayo Orogen was likely the result of collisional interactions with the Sveconorwegian province of Baltica, in contrast to previously proposed models that place this margin of Amazonia as the conjugate of the Grenville province of Laurentia. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Rodinia was assembled. In South America the Amazon Craton is the largest of the Precambrian blocks that constitute the continental Many reconstructions for the early Neoproterozoic platform (Tassinari and Macambira, 1999), and its role in the super- supercontinent Rodinia predict interactions between a continent cycle has for long been recognized (Cordani et al., 2009). Laurentia–Baltica–Amazonia triple joint along internal collisional Records of the participation of Amazonia in the supercontinent orogens (e.g. Hoffman, 1991 or Li et al., 2008 for a recent review). Rodinia are expressed as: (a) metamorphosed passive-margin and These different orogenic segments developed diachronously dur- rift sequences of the Sunsás-Aguapei and Nova Brasilandia belts in ing late Mesoproterozoic to early Neoproterozoic times, and their western Brazil – eastern Bolivia (review by Teixeira et al., 2010), timing defines the chronology for the collisional interactions that (b) scattered intracratonic magmatic events and shear-zones took place between different crustal blocks and microcontinents as developed obliquely with respect to the colliding margin (review by Cordani et al., 2010), and (c) paleomagnetic evidences obtained from late Mesoproterozoic volcanic and sedimentary rocks of the ∗ Rondonia region in Brazil indicating proximity and interaction of Corresponding author. this margin of Amazonia with respect to (modern) SE Laurentia E-mail address: [email protected] (M. Ibanez-Mejia). 0301-9268/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.precamres.2011.09.005 M. Ibanez-Mejia et al. / Precambrian Research 191 (2011) 58–77 59 (Tohver et al., 2002; D’Agrella-Filho et al., 2008). Although the with autochthonous Amazonia basement, improves our knowledge involvement of Amazonia in Rodinia is in general a well-accepted about the evolution of the Proterozoic orogens of South America hypothesis (e.g. Li et al., 2008), many details and questions and provides an additional piercing point in Amazonia for estab- regarding intercratonic orogen correlations and the evolution of lishing intercratonic correlations with other late Meso- to early Meso-Neoproterozoic collisional belts of the Amazon Craton are Neoproterozoic orogens worldwide. far from being resolved. An example of this issue is the observation that the Sunsás margin of Amazonia has been correlated by differ- 2. Geological setting – known provinces of the Amazon ent authors with virtually every segment of the Grenville margin of Craton Laurentia (see Tohver et al., 2004a, and references therein), in part due to the fact that the lack of geological and robust geochrono- The Amazon Craton has been broadly subdivided in six different logical information from northwestern South America has left its Precambrian provinces (Fig. 1) and its evolution spans over 2 Ga of role in many of these reconstructions mostly unconstrained. Earth’s history. A detailed discussion about the general crustal con- As a result of dense vegetation cover, heavy tropical weather- figuration of the Amazon Craton is beyond the scope of this paper ing, and the development of Phanerozoic sedimentary basins, there and only a brief summary of most relevant events are presented are still sizable areas in northern South America where its Pre- below. The interested reader is referred to the works of Teixeira cambrian basement remains poorly studied or even completely et al. (1989), Tassinari and Macambira (1999), Santos et al. (2000), unknown. This is the case of the north Andean foreland basins, Cordani and Teixeira (2007), and Santos et al. (2008) for a more in where a large portion of northern Venezuela, eastern Colombia, depth discussion on this subject. In general, it is thought that after eastern Ecuador and eastern Peru (Fig. 1) comprise an area in excess 2 the amalgamation of Archean microcontinents along the Maroni- of 800,000 km of covered basement. However, with the exception Itacaiunas (MI) province during the Transamazonian orogeny, the of K–Ar and Rb–Sr ages from wells presented by Kovach et al. (1976) Ventuari-Tapajos (VT) and Rio Negro-Juruena (RNJ) belts evolved and Feo-Codecido et al. (1984) nothing else is known about the through the continuous accretion of intraoceanic arcs to this proto- geochronology of this vast region. Amazonia nucleus. The two marginal provinces located towards Paleogeographic models that juxtapose the Sunsás margin of the southwestern portion of the craton, the Rondonia-San Ignacio Amazonia against southeastern Laurentia implicitly predict that the (RSI) and the Sunsás-Aguapei (SA), are the result of accretionary Meso-Neoproterozoic orogen of the Amazon Craton should extend and collisional tectonics that took place throughout the Mesopro- north of the Sunsás-Aguapei orogen, partly as a conjugate margin terozoic (Sadowski and Bettencourt, 1996; Cordani and Teixeira, to the Laurentian Grenville province under the Amazon River basin, 2007). and possibly by interaction with a third continental mass even fur- The RSI orogeny, which took place during the time interval from ther north (e.g. Hoffman, 1991; Tohver et al., 2002, 2006; Fuck ca. 1.56 to 1.30 Ga, is characterized by the accretion of early Meso- et al., 2008; Li et al., 2008; Cardona et al., 2010). This interpreta- proterozoic arc terranes overprinted by high-grade metamorphism tion has benefited from the occurrence of high-grade metamorphic during the mid Mesoproterozoic by inferred collision of a micro- inliers included within the north Andean orogen in Colombia such continent – the Paragua block – against the RNJ continental margin as the Garzón and Santa Marta massifs, among others (Restrepo- (Bettencourt et al., 2010). Collision of the Paragua block against Pace et al., 1997; Cordani et al., 2005; Ordonez-Carmona et al., 2006; Amazonia resulted in high-grade metamorphism of the Chiqui- Cardona et al., 2010). However, given the complex deformational tania gneisses and the Lomas Manechis granulites at about 1.33 Ga history of the northern Andes (Aleman and Ramos, 2000), in partic- (Bettencourt et al., 2010; Santos et al., 2008), also coinciding with ular its strong Meso-Cenozoic margin-parallel strike-slip transport cessation of arc magmatism